The term serial printer is generally applied to printing devices that print one character at a time in linear arrangement on a paper medium, the linear arrangement of the printed characters being effectuated by moving an actuatable printing element relative to the paper medium, or by moving the paper medium relative to the printing element.
Known serial printers have commonly provided an impactable hammer that is disposed in cooperating relationship with a differentially positionable and divergently formed printing element, the printing element varying in configuration as between a type bar or stick, a type sector or wheel, a type ball or sphere, and a cylindrical drum along the peripheral surface of which the hammer is transversely activated. Although these known types of serial printers have proven effective in satisfying the requirements of particular and isolated printing tasks, none has succeeded in fully overcoming all of the limitations that have been experienced with serial printers as a class, such limitations including excessive manufacturing cost, relative slowness in printing speed, and insufficiency in the size of the character set that may be arranged on conventional printing elements, be they type bars, wheels, or print balls. Specifically, serial printers equipped with single type bars, sectors or wheels have proven ineffective for use as an alphanumeric serial printer, due to the limited number of type characters that can be arranged on such single printing elements. Serial printers equipped with print balls, on the other hand, although commonly providing a minimal character set suitable for alphanumeric printing, have generally proven to be inefficient from the standpoint of the printing speeds that are attainable thereby, due to the requirement that such balls be both rotatably and tiltably activated during each printing cycle. Serial printers providing a transversely movable hammer and a rotating drum have additionally proven to be exceedingly costly to manufacture, due primarily to the cost of building the print drum.